(CNN) -- Ten American sailors are missing after a US Navy guided-missile destroyer collided early Monday with an oil tanker east of Singapore, the fourth accident this year involving a US warship in Asian waters.

The Navy's 7th Fleet said the USS John S. McCain collided with the merchant vessel Alnic MC while the destroyer was making its way to a port in Singapore. The collision was reported at 5:24 a.m. local time, east of the Malacca Strait, one of the world's most congested shipping routes.

The Navy reported significant hull damage to the McCain, saying there was flooding in berthing compartments as well as machinery and communication rooms.

Following the accident, President Donald Trump arrived at the White House on Marine One and told reporters of the collision, "That's too bad." He and Vice President Mike Pence also tweeted that their thoughts and prayers were with the sailors aboard the destroyer.

Sen. John McCain joined them and thanked the rescue crews for their service. The destroyer is named for the senator's father and grandfather, both of whom were Navy admirals. The senator was a captain in the Navy.

A US 7th Fleet spokesman said the McCain is one of 14 Aegis-equipped ships the Navy has forward-deployed to Japan and it plans to add another next year. The US Navy has 84 vessels equipped with the Aegis system.

Cmdr. Clay Doss said the United States has a mixture of ships and aircraft available to cover all missions even without the McCain or USS Fitzgerald, the McCain's sister ship that was damaged in a June collision.

The US military and South Korea began 10-day military exercises Monday, as scheduled. The annual drills antagonize Pyongyang, which issued a statement Sunday that military exercises are "reckless behavior driving the situation into the uncontrollable phase of a nuclear war."

In addition to the 10 missing sailors, the Navy said five were injured in the collision. Four of those were flown by a Singapore navy helicopter to a hospital in Singapore, where they were treated for injuries not considered life-threatening, the Navy said.

US helicopters and Marine Corps Osprey aircraft from the amphibious assault ship USS America were joining search-and-rescue efforts along with Singaporean ships and helicopters, the Navy said.

Rocky year for Navy

The McCain collision marks the fourth incident involving a US Navy warship in the Pacific this year.

On June 17, the USS Fitzgerald collided with a container ship off the coast of Japan. That collision resulted in the deaths of seven US sailors. The Fitzgerald will be transported to the United States for repairs.

Experts: 'Navy is not looking good'

Military experts said the latest incident calls into question the Navy's training and will likely lead to changes in the Navy's leadership.

"I can almost guarantee you that there will be a tumultuous shake-up in the senior leadership of at least the 7th Fleet and maybe the Navy in general," CNN military analyst Rick Francona said.

"The Navy is not looking good about now, especially when we need those ... Aegis-equipped ships for possible ballistic missile defense in a North Korean scenario," he added.

In a report on the Fitzgerald collision released last week, the Navy said it would review its training and qualification procedures.

"The collision was avoidable and both ships demonstrated poor seamanship. Within Fitzgerald, flawed watch stander teamwork and inadequate leadership contributed to the collision," a 7th Fleet statement said.

Oil tanker 'three times bigger'

Carl Schuster, a former director of operations at the US Pacific Command's Joint Intelligence Center, said the oil tanker would have been at least three times bigger than the USS John S. McCain.

"Oil tankers are huge, and it takes miles for them to change course," he said.

"When you're going into a congested channel, you're supposed to be very alert, track ships around you to a very meticulous degree."

The Malacca Strait, which runs between Indonesia, Malaysia and Singapore, is the world's second-busiest waterway, according to the World Economic Forum. The collision took place in waters to the east of the Malacca Strait, US authorities said.

At a press conference, Malaysian authorities said both ships were heading toward Singapore from the South China Sea when the collision occurred. They described the area as very busy, with some 80,000 ships passing through it every year.

Both ships should have reported to what the Malaysian authorities called a maritime "traffic separation scheme," essentially air traffic control for ships.

Francona said no matter what the tanker did, the faster, nimbler US destroyer should have been able to avoid a collision.

The Maritime and Port Authority of Singapore said the Alnic sustained damage to a tank at its bow, about 7 meters (23 feet) above the waterline. No one was injured on the tanker, it said, and no oil spill was reported.